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Electrical issues on ‘79 special

Discussion in 'The Garage' started by RatSpecial, Apr 28, 2019.

  1. RatSpecial

    RatSpecial XS650 Member

    Hey all, about a month ago I bought a ‘79 special that’s been chopped into a cafe racer that I knew was gonna be a little bit of work but I kinda jumped into the deep end with this one. Long story short; went out for a ride last week about 40 miles round trip(that’s as far as I got) when I tried to take off from a light and everything died. Figured it was the battery since the guy I bought it from said it had sat all winter and he couldn’t get it started. Bought a new battery and found out my main fuse was blown(go figure). Unplugged the headlight looking for bad connections also, put a new main fuse in and all my lights came back on. Plugged the headlight in and everything went dark again.
    So I guess my question is, is this a problem with my headlight or a bad connection somewhere else along the wiring?
    This is my first xs650 so i really have no idea where to start or what the problem even could be. Thanks in advance! Pic for attention
     

    Attached Files:

  2. Downeaster

    Downeaster Everything in XS Top Contributor

    Unfortunately, the answer is "Yes".

    Meaning it could be either the headlight assembly or the wiring leading to it. Something is shorting to ground, either inside the socket, or somewhere between the battery and the headlight.

    The fact that it works until you plug in the headlight most likely means it isn't a "hard short" with a bare wire touching ground. If that were the case, it would blow the fuse with or without the light.

    First thing to do is disconnect the light, get a meter and check voltages at the pins on the harness side of the connector. Also, wiggle things around vigorously while checking, looking for large variations in the voltage or another blown fuse.

    Also check for a short from one of the pins on the headlight assembly to ground. You'll see small values across the filaments (from pin to pin on the bulb socket, but you shouldn't see anything to the frame of the headlight (As best I can remember anyway.)
     
    RatSpecial and peanut like this.
  3. RatSpecial

    RatSpecial XS650 Member

    Thanks for the quick reply! I ended up removing all the fuses and unplugging the headlight and then put all the fuses back in while leaving the headlight off. Fired right up after about 3-5 kicks(it’s been sitting for a week), checked the voltage at the battery terminals while it’s running and it had wild fluctuations from 11.9 up to about 18.5, same with the headlight plug itself. I’m guessing this is more indicative of a bad harness somewhere?
     
  4. peanut

    peanut XS650 Guru Top Contributor

    more likely a bad regulator with that voltage . max charging voltage should be around 14.5v at 3000rpm I believe but check the manual.
    Is your regulator present and connected ?
     
    RatSpecial and Downeaster like this.
  5. RatSpecial

    RatSpecial XS650 Member

    It is indeed and looks to be one of the newer/shinier parts on the bike, I’m guessing it was replaced when they turned it into a cafe racer? I’m just at a loss because it was running great up until a week ago when it died. I did have to refill the cells on the old battery a few times so now I’m wondering if it was overcharging and frying the cells?
     
  6. peanut

    peanut XS650 Guru Top Contributor

    thats exactly what it sounds like...... mind you if your headlight fuse had blown there would have been no load on the charging system which would not be good for the regulator .Its definitely fubar if you are seeing 18v

    hey welcome to the forum by the way. You'll get a better response later when the rest of the World has woken up lol
     
    RatSpecial likes this.
  7. RatSpecial

    RatSpecial XS650 Member

    Alright so new regulator is going on the parts list. Can I reuse the wiring from it? The regulator and wires are probably the newest things on the bike, or should I just use new wires with the new regulator?
    Also, is there anything that would cause the regulator to fail? It does seem pretty new
     
  8. RatSpecial

    RatSpecial XS650 Member

    But also thanks, good to finally join the club lol my dad has his ‘72 xs650 that he bought when he graduated high school sitting in his garage and I’m hoping this one will motivate him to fix his lol
     
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  9. peanut

    peanut XS650 Guru Top Contributor

    72 eh .... rare and valuable bike It would be a good project for you to do together ;)
    I never had the opportunity with my old man .......he hated me lol
     
  10. peanut

    peanut XS650 Guru Top Contributor


    it very difficult to know what to advise as your wiring and components are clearly non original and have been hacked about by the previous owner.

    I would say that your best bet is to get a multimeter and start testing the charging system wiring and components. Pictures of your regulator and alternator would sure help us advise you
     
    RatSpecial likes this.
  11. Brassneck

    Brassneck XS650 Guru

    Are you running points? I think the early '79 would have had the older ignition and older charging set up, whereas the later '79 would have had the newer ignition (TCI) and charging set up...so if/when you replace your regulator/rectifier (assuming you get a combo unit), I think you want to be sure to get the correct one. Or maybe that changed in '80? I can't recall, but it's easy to mix up them up (and they look about the same).
     
    peanut likes this.
  12. RatSpecial

    RatSpecial XS650 Member

    I’ll snap some pics tonight when I make it home from work. I’m workin two jobs right now so I’m away from my house most of the day lol I’m gonna give the shop that did the work on the bike a call when I can also and see if they have any ideas what might be causing the issues. Luckily they aren’t too far and worse comes to worse I can trailer it there and see if he’d be willing to clean up the wiring at all.
    Yeah he bought his right out of high school and put 60k miles on it before he put it away in ‘91 with a full tank of gas since I guess having a kid will do that lol
     
  13. RatSpecial

    RatSpecial XS650 Member

    It is running on the points, we cleaned and sanded them the first week trying to get the second cylinder to fire. Turns out it was a bad coil pack and easy fix for that problem lol
     
    Brassneck likes this.
  14. 5twins

    5twins XS650 Guru Top Contributor

    17,135
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    You will need to positively identify the charging system you have. The stock '70-'79 system differs from the stock '80-'83 system, and the aftermarket PMA system is different from both of those. All 3 use a different type of regulator.
     
  15. RatSpecial

    RatSpecial XS650 Member

    Sorry for the late post for pictures, work has been kickin my ass this week. I snapped a couple of the regulator and fuse box and the battery itself, didn’t take the tank off just yet because I’m hoping that the problems are easy to get to lol I included the headlight birds nest just so you can see what I’m dealing with. The more I dive into this the more I start wondering what the guy I bought the bike from paid to have done?
     

    Attached Files:

  16. XSLeo

    XSLeo XS650 Guru Top Contributor

    One pic you didn't get is of the alternator.
    remove the round cover on the left side that has Yamaha cast into it.
    Under there is your alternator.
    That way we can tell more about what it is. Being a 79 it should have one style of brush holder. In 80 it changed to a different style.
    If a PMA that's a horse of a different color.
    Leo
     
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  17. RatSpecial

    RatSpecial XS650 Member

    whoops lol I do remember the guy I bought the bike from saying that it was a new stator but now that I’m having issues with other “new” parts I’m wondering how new they actually are
     

    Attached Files:

    gggGary likes this.
  18. RatSpecial

    RatSpecial XS650 Member

    Alright so, small update. Replaced the regulator with a rectifier/regulator from dime city, started up on the first kick and voltage stayed consistent and charged the battery(yay!) but about 1/4 mile down the road and had a small electrical fire from what looks like the relay box? I believe it’s just because it was a 40 year old wire and grounded somewhere along the body?
     
  19. peanut

    peanut XS650 Guru Top Contributor

    which relay box would that be ;)
    A picture would help us identify what you are referring to :)
     
  20. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    [​IMG]
    I'm guessing that picture shows part of your problems, or at least very poor wire color choices, LOL.
    That type brush block requires a voltage regulator designed for and wired like this.

    early charging diagram.jpg
     
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